This invention relates generally to distortion measurement systems and, more particularly, to distortion measurement of spacecraft structures in applications that require extremely precise dimensional relationships. Many spacecraft have a significant problem in that their on-orbit shape may be distorted from an ideal desired shape. The differences may be due to thermal distortion, manufacturing tolerances, alignment tolerances, deployment tolerances, or other sources. Distortions in shape can cause performance degradation in spacecraft applications that depend on precise dimensional relationships. For example, the spacing of antenna elements or other sensors may be critical to the results obtained in a particular application. In most cases, this degradation in performance could be corrected if the distortions could be accurately measured. If accurate measurements could be obtained, the effects of distortion could be removed either by calibration, i.e., by making adjustments to resultant data on the spacecraft or on the ground, or by shape adjustment using on-board actuators. Prior to the present invention, spacecraft structures for which distortion is a known problem have been designed to be as near to distortion-free as possible. In most cases, this approach imposes a penalty of increased weight and cost.
Although the problem and its solutions are described in this specification in relation to a spacecraft application, it will be readily understood that distortion measurement problems may also arise in other contexts. It will appreciated from the foregoing that there is a need for a system that can measure distortion, particularly of spacecraft structures, and make appropriate adjustments. The current invention proposes a unique way for measuring spacecraft distortions and making the appropriate adjustments to improve alignment and/or structural distortions. This unique method allows the measurements to be made rapidly enough to measure and correct dynamic distortions and also allows the more efficient use of limited illumination capability.